The authors address the problem of free carrier screening of exciton states in two-dimensional monolayer semiconductors. Basic theoretical considerations are presented concerning the applicability of the commonly used static approximation of the screening effect and the implications are discussed. The authors show that the low-frequency models leads to a major overestimation of the free carrier response and are inadequate to describe the screening of strongly bound excitons in monolayer materials. The presented arguments are consistent with existing high-level many-body theories and transparently illustrate the underlying physics.